error in preparsed UCD: '%s' is not a valid Unicode string o

Error message

error in preparsed UCD: '%s' is not a valid Unicode string on line %ld

What it means

Thrown by PreparsedUCD::parseString() when u_parseString() fails to parse the input as a valid Unicode string after attempting both an initial parse and a buffer-overflow retry with an enlarged buffer. This function is used for multi-character string properties like Case_Folding, Lowercase_Mapping, Titlecase_Mapping, and Uppercase_Mapping. Note: this error does not set errorCode itself — it only reports the pre-existing U_FAILURE from u_parseString.

Source

Thrown at deps/icu-small/source/tools/toolutil/ppucd.cpp:559

    }
    start = static_cast<UChar32>(st);
    end = static_cast<UChar32>(e);
    return true;
}

void
PreparsedUCD::parseString(const char *s, UnicodeString &uni, UErrorCode &errorCode) {
    char16_t *buffer=toUCharPtr(uni.getBuffer(-1));
    int32_t length=u_parseString(s, buffer, uni.getCapacity(), nullptr, &errorCode);
    if(errorCode==U_BUFFER_OVERFLOW_ERROR) {
        errorCode=U_ZERO_ERROR;
        uni.releaseBuffer(0);
        buffer=toUCharPtr(uni.getBuffer(length));
        length=u_parseString(s, buffer, uni.getCapacity(), nullptr, &errorCode);
    }
    uni.releaseBuffer(length);
    if(U_FAILURE(errorCode)) {
        fprintf(stderr,
                "error in preparsed UCD: '%s' is not a valid Unicode string on line %ld\n",
                s, static_cast<long>(lineNumber));
    }
}

void
PreparsedUCD::parseScriptExtensions(const char *s, UnicodeSet &scx, UErrorCode &errorCode) {
    if(U_FAILURE(errorCode)) { return; }
    scx.clear();
    CharString scString;
    for(;;) {
        const char *scs;
        const char *scLimit=strchr(s, ' ');
        if(scLimit!=nullptr) {
            scs = scString.clear().append(s, static_cast<int32_t>(scLimit - s), errorCode).data();
            if(U_FAILURE(errorCode)) { return; }
        } else {
            scs=s;

View on GitHub (pinned to 1b2de5e052)

Solutions

Ensure string property values use the correct format: space-separated hexadecimal UTF-16 code units.
Verify there are no stray characters, missing spaces, or incomplete code unit pairs in the field.
Cross-reference with official Unicode case mapping data to verify the expected value format.
Check for BOM or encoding issues in the ppucd file that could corrupt string fields.

Example fix

// before
00DF;Lowercase_Mapping=00DF;...
// after
00DF;Lowercase_Mapping=00DF;...
// For multi-char mappings, use space-separated units:
// before: Case_Folding=00730073
// after:  Case_Folding=0073 0073

Defensive patterns

Strategy: validation

Validate before calling

// Pre-validate string property fields as space-separated hex code units
#include <cstring>
#include <cstdlib>

bool isValidUnicodeStringField(const char* s) {
    if (s == nullptr || *s == '\0') return false; // empty may be valid for some properties
    const char* p = s;
    while (*p) {
        // Skip leading spaces
        while (*p == ' ') p++;
        if (*p == '\0') break;
        // Parse hex code unit
        char* end;
        strtoul(p, &end, 16);
        if (end == p) return false; // not a hex digit
        p = end;
    }
    return true;
}

Prevention

Ensure string property values are space-separated hexadecimal UTF-16 code units.
Do not use raw UTF-8 text or other encodings in string property fields.
Validate string field formatting before building ICU data.

When it happens

Trigger: A ppucd string property field contains malformed escape sequences or invalid UTF-like syntax. u_parseString expects a specific format (typically space-separated hex code units); any deviation causes failure. The error is triggered for fields like 'lc=', 'uc=', 'tc=', 'cf=' with invalid content.

Common situations: Missing or incorrect space separators between code units in string fields; using raw UTF-8 text instead of hex-encoded code units; truncated escape sequences; encoding issues in the ppucd file.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/80f33f8cc29c305b. Report an issue: GitHub.